President Bashar al-Assad met for the first time with Serge Brammertz, the head of the United Nations investigation into the truck-bomb murder of former Prime Minister Rafiq Hariri of Lebanon in Beirut last year. The meeting in Damascus follows allegations made in January by Abdel-Halim Khaddam, the long-serving former vice president of Syria, that Mr. Assad had threatened Mr. Hariri before he was assassinated. No other details of the meeting were provided. Syria has denied any involvement; Mr. Assad had earlier refused requests for an interview.